Optical connector ferrule filled with adhesive

Abstract: The present invention relates to an adhesive for connecting and fixing an optical fiber to an optical connector and to an optical connector which uses that adhesive. The adhesive prevents deformation of the optical connector ferrule and stressing of the optical fiber due to hardening shrinkage during the hardening of the adhesive and/or a shrinkage during cooling of the adhesive. In accordance with the invention, (1) the value of (the coefficient of linear expansion (°C⁻¹) of the adhesive) x (the difference between a hardening temperature of the adhesive and room temperature (°C)) x (Young's Modulus (kg/mm²) of the adhesive) is equal to or less than about 2.5, (2) the value of (the rate of hardening shrinkage (%) of the adhesive) x (Young's Modulus (kg/mm²) of the adhesive) is equal to or less than about 1000 and/or (3) the adhesive hardens at room temperature.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates a multi-fiber optical connector ferrule where the optical fibers are fixed to the optical connector ferrule by an adhesive. 2. Description of the Related Art The general shape of an optical connector ferrule, especially a multi-fiber optical connector ferrule, is shown in FIGURE 1. For example, after an optical fiber cable including four optical fibers is inserted into an optical fiber cable insert hole 5 and each of the fibers in inserted into an optical fiber insert hole 4, a thermosetting epoxy type adhesive 8 is injected into an adhesive injection opening 2. Generally, one optical fiber cable includes up to 1000 optical fibers. The adhesive 8 is hardened at about 80°C so that the optical fiber is fixed to the ferrule 1. Thereafter, the end portion of the ferrule is ground to form an optical connector. As shown, a plurality of fixing pin insert holes 3 are provided for receiving fixing pins to connect to another optical connector. FIGURE 2 is a cross sectional view taken along line II-II of FIGURE 1 and wherein the adhesive 8 has been injected into the adhesive injection opening 2. The adhesive needs to have a low viscosity to fill up to the end of the optical fiber holes 4 and a high hardness to fix the optical fiber tightly when the ferrule 1 is ground. In addition, conventionally, the thermosetting epoxy type adhesive used is selected to provide resistance to chemicals or the like. ("Optoronics" No. 3, pages 103 to 106, published in 1991) Specifically, in the conventional adhesive, the coefficient of linear expansion is from 5.0 x 10 -5 to 1.0 x 10 -4 , Young's Modulus is from 500 to 1000 kg/mm 2 , the hardening temperature is from 60°C to 100 °C, the filler content is from 0 weight % to 30 weight %, the viscosity at the hardening temperature is 100 cps to 1000 cps, the particle diameter of the filler is from 0.1 µm to 100 µm, and the rate of hardening shrinkage is 1 % to 5%. However, the conventional adhesive has had the problem(s) that the ferrule may be deformed and that the optical fiber is stressed, thereby increasing light transmission loss, by the shrinkage force of the adhesive during cooling down from the hardening temperature to room temperature, or a shrinkage after hardening. A different type of connector ferrule is known from EP-A-434 212, showing an optical fiber being fixed within a bore of the ferrule by a thermo-plastic adhesive. SUMMARY OF THE INVENTION As a result of an examination of the above problems, it was recognized, in accordance with the present invention that the rate of hardening shrinkage and Young's Modulus of the adhesive have to be small to prevent deformation of the ferrule and to minimize stress to the optical fiber. The object of the present invention is solved by a multi-fiber optical connector ferrule having the features set out in claim 1. Other objects, features and characteristics of the present invention, as well as the functions of the related elements of the structure, and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIGURE 1 is a perspective view showing an optical connector ferrule; FIGURE 2 is a cross sectional view taken along line II-II of FIGURE 1; and FIGURE 3. is a perspective view showing an optical connector produced using an adhesive in accordance with the present invention. DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS The present invention will be described in detail as follows: In the adhesive of present invention, the value of (the harding shrinkage (%))) x (Young's Modulus (kg/mm 2 ) is 1000 or less and, especially, the rate of hardening shrinkage is preferably 1% or less and the Young's Modulus is preferably from 100 kg/mm 2 to 1000 kg/mm 2 . Since the adhesive of the present invention has a small rate of hardening shrinkage and Young's modulus, it is unlikely that it will deform the ferrule during hardening of the adhesive and or that the adhesive will increase the light transmission loss by stressing the optical fiber. If the Young's modulus of the adhesive of the present invention is more than 100 kg/mm 2 , the ferrule material and the optical fiber are stressed to deform and thus there is an increase in the light transmission loss. Furthermore, if the Young's Modulus of the adhesive is less than 100 kg/mm 2 , it is too soft and cannot support the optical fiber sufficiently when the optical fiber is ground. The presence of filler in the adhesive causes the adhesive to have a low rate of hardening shrinkage. The filler content is preferably from about 20 weight % to 70 weight %. However, generally, the filler increases the viscosity of the adhesive. Accordingly, the adhesive preferably includes a spherical filler the diameter of which is from 0.1 µm to 1.0 µm so as to have a good fluidity and to flow to the end of the optical fiber insert holes. A diameter of more than 1.0 µm does not contribute to fluidity A diameter of less than 0.1 µm coheres too easily. Furthermore, if the filler content is less than about 20 weight %, it is not possible to decrease the hardening shrinkage and the coefficient of linear expansion. If the content is more than about 70 weight %, the adhesive is too viscous. Silica, calcium carbonate, alumina, mica or the like are preferable for the filler of the adhesive of the present invention. The viscosity of adhesive is preferably from 50 cps to 2000 cps at the hardening temperature. If the viscosity is less than 50 cps, the adhesive is too fluid and is thus hard to work with. Preferably, the adhesive of the present invention is an epoxy type adhesive, silicone type adhesive, acryle type adhesive or the like. A four-fiber optical connector ferrule, as shown in FIGURE 1, was molded by transfer molding. A tape-like coated optical fiber, in which four optical fibers were disposed in parallel, was inserted into the ferrule, and each of the eight kinds of epoxy type adhesive indicated in Table I including a filler comprising a silica, was injected from an adhesive injection opening 2. Thereafter, it was hardened at 80°C for 1 hour so as to adhere and fix an optical fiber. Then, the deformation volume at a wavelength of 1.3 µm was measured. The results of the measurements are indicated in Table I. The adhesive having a viscosity of less than 50 cps was so fluid that it was difficult to fix the optical fiber. The adhesive having a viscosity of more than 2000 cps did not flow to the end of the optical fiber insert hole(s). Furthermore, a filler, the diameter of which was from 0.1 µm to 1.0 µm, was used so that the hardening shrinkage was less than 0.1 µm and the viscosity was less than 2000 cps. Comparative Example 1 A four-fiber optical connector ferrule as shown in FIGURE 1 was molded by transfer molding, as in Embodiment 3-1. A tape-like coated optical fiber, in which four optical fibers were disposed in parallel, was inserted into the ferrule, and an epoxy type adhesive, including an alopaticamine type hardening agent, was mixed and injected from an adhesive injection opening 2. Thereafter it was hardened at 80 °C for 2 hours and cooled down to room temperature so as to form an optical connector as shown in FIGURE 3. The deformation volume thereof was less than 0.5 µm and the light transmission loss thereof was less than 0.3 dB. As described above, according to the present invention, since the value of (the rate of the hardening shrinkage (%)) x (Young's Modulus (kg/mm 2 )) is 1000 or less, the deformation volume of the ferrule during hardening is small and little stress is given to the optical fiber, so as to prevent light transmission loss. In addition, since the filler of the adhesive has a small diameter and the viscosity thereof is from 50 cps to 2000 cps, the adhesive flows sufficiently to the end of the optical fiber insert holes and has sufficient hardness so that the optical fiber is not broken during grinding. It has thus been demonstrated that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention and are subject to change without departure from such principles.

Claims: A multi-fiber optical connector ferrule having an adhesive injection opening (2) for giving access to the optical fibers and being filled with an adhesive for connecting and fixing the optical fibers to the ferrule, wherein the adhesive is a curring and hardening type adhesive and has a value of the product of the rate of hardening shrinkage in % x the Young's modulus in (kg/mm 2 ) ≤ 1000, wherein the rate of hardening shrinkage is equal to or less than about 1%, and in that a viscosity of the adhesive at a hardening temperature is from about 50 mPa·S (50 cps) to about 2000 mPa·S (2000 cps). An optical connector ferrule according to claim 1, wherein the Young's Modulus is from about 100 kg/mm 2 to about 1000kg/mm 2 . An optical connector ferrule according to claim 1, wherein the adhesive includes from about 20 weight % to about 70 weight % filler. An optical connector ferrule according to claim 3, wherein a grain diameter of the filler is from about 0.1 µm to about 1.0 µm.

Inventors: HONJO MAKOTO, KATSURA HIROSHI, UEDA TOMOHIKO, YAMANISHI TORU, HONJO, MAKOTO, KATSURA, HIROSHI, UEDA, TOMOHIKO, YAMANISHI, TORU, HONJO, MAKOTO, C/O YOKOHAMA WORKS OF, KATSURA, HIROSHI, C/O YOKOHAMA WORKS OF, UEDA, TOMOHIKO, C/O YOKOHAMA WORKS OF, YAMANISHI, TORU, C/O YOKOHAMA WORKS OF
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1994
Main classification: G02B6
IPC codes: G02B6